The occasional "smell" at Alcudia Beach (Mallorca) is almost always caused by decaying Posidonia oceanica, a type of Mediterranean seagrass. While this seagrass is a vital part of the ecosystem—it protects the beach from erosion and keeps the water crystal clear—it can wash ashore in large clumps known as "banquettes." When these mounds of seagrass begin to decompose in the hot 2026 Spanish sun, they release a strong, sulfur-like odor that many tourists mistake for sewage. Furthermore, because Alcudia is a very shallow, "horseshoe" bay with low wave action, the water can become stagnant in the summer, trapping organic matter. Local authorities often leave the seagrass on the sand because removing it can actually destroy the beach's natural defenses. The smell is usually temporary and is actually a sign of a very healthy, oxygen-rich marine environment, even if it isn't particularly pleasant for your morning walk.